1. Field of the Invention
The present invention relates to a method and an apparatus for magnetically transferring information from a master medium bearing the information to a slave medium.
2. Description of the Prior Art
A magnetic transfer method is one in which magnetic patterns corresponding to information (e.g., servo signals) recorded in a master medium are transferred by applying a transfer magnetic field in a state where the master medium and a slave medium are in close contact with each other. Such a magnetic transfer method is disclosed, for example, in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, 10(1998)-269566, and so on.
Incidentally, during the magnetic transfer by the foregoing magnetic-transfer method, the repeated use of the master medium causes dust to be stuck to the surface of the master medium, resulting in contamination thereof. As dust to be stuck to the master medium, that which is generated in a surrounding environment, chips of the master and slave media generated by contact therebetween may be mentioned.
If the magnetic transfer is carried out in a state where the dust is stuck to the master medium, close contact cannot be secured between the master medium and the slave medium in an area ranging from the dust stuck portion as a center to a periphery, and pattern transfer of a predetermined signal level cannot be executed. Consequently, the magnetic transfer quality is reduced. If a recorded signal is a servo signal, then a satisfactory tracking function cannot be obtained. Thus, there has been a problem of reduced reliability in the conventional case.
The adhesive power of the dust stuck to the surface of the master medium is increased due to the repeated close contact between the master medium and the slave medium. Therefore, in all the slave media magnetically transferred thereafter, similar or greater pattern transfer failures occur, causing the production of a large number of defective articles. In addition, such stuck objects result in the deformation of the surface of the master medium, thus causing a loss of normal function thereof.
The present invention was made in view of the foregoing problems, and an object of the present invention is to provide a method and an apparatus for magnetic transfer, capable of performing highly reliable magnetic transfer by preventing the degradation of transfer quality caused by dust in close contact between the master medium and the slave medium.
In order to achieve the foregoing object, in accordance with the present invention, a magnetic transfer method is provided for performing magnetic transfer by bringing a master medium bearing an information signal and a slave medium into close contact with each other, and then applying a transfer magnetic field. In this case, the magnetic transfer method comprises the steps of: preparing a plurality of master media; replacing the master medium after magnetic transfer is executed a predetermined number of times; and cleaning the replaced master medium.
In accordance with the present invention, a magnetic transfer apparatus is provided for performing magnetic transfer by bringing a master medium bearing an information signal and a slave medium into close contact with each other, then applying a transfer magnetic field. In this case, the magnetic transfer apparatus comprises: magnetic transfer means for performing magnetic transfer in a state of close contact between the master medium and the slave medium; replacing means for preparing a plurality of master media, and replacing a master medium after magnetic transfer is executed a predetermined number of times; and cleaning means for cleaning the replaced master medium.
The cleaning of the master medium should preferably be performed by replacing a master medium for each magnetic transfer process. Specifically, preferred cleaning is one performed based on a wet process by washing liquid, which uses alcohol, pure water or organic solvent. Especially, ultrasonic washing is preferable. In addition, cleaning by air blowing, especially electrostatic air blowing, may be employed, and wiping cleaning by using a wiping material may also be employed.
To prevent the peeling-off of a magnetic film or the like from the master medium caused by the cleaning, the adhesive power of this thin metal film to a substrate or the like should preferably be set equal to 1xc3x97109 N/m2 or higher.
A preferred magnetic transfer method is one designed to perform magnetic transfer in the following manner. Specifically, the slave medium is subjected to DC magnetization in a track direction, and this slave medium and a magnetic transfer master medium, on which a magnetic layer is formed into micro uneven patterns corresponding to information to be transferred, are brought into close contact with each other, then applying a transfer magnetic field in a direction roughly reverse to the initial DC magnetizing direction of the slave medium. As to the aforementioned information to be transferred, a servo signal is preferred.
According to the present invention, a plurality of master media are prepared and the master medium is replaced and cleaned after magnetic transfer is performed a predetermined number of times, whereby the quantity of dust stuck to the master medium can be reduced. Therefore, it becomes possible to prevent the degradation of a transfer signal caused by a failure of close contact between the master medium and the slave medium due to objects stuck therebetween, and to execute magnetic transfer with stable quality. Thus, the reliability thereof can be improved.